Wet chemical etching is widely used for fabrication of semiconductor wafers. And, wet etchings in single wafer processing tool are dominant for advanced technology nodes compared wet etching in batch processing tool. Typically, the wafer is mounted on a rotating wafer-receiving surface and a liquid etchant is applied to the wafer through a nozzle positioned above the wafer. The nozzle can be at a fixed position over one location such as the rotational center of the wafer-receiving surface, and thus the center of the wafer, or the nozzle can be a scanning nozzle that scans between the rotational center and the peripheral edge of the wafer-receiving surface. As the wafer is rotated by the wafer-receiving surface, centrifugal force distributes the liquid etchant along the surface of the wafer.
The wafer-receiving surface is heated to promote the etching action on the wafer. However, the temperature of the wafer-receiving surface is not uniform across the surface. Because of the heat loss to the ambient along the peripheral edge of the wafer-receiving surface, there is a temperature gradient in radial direction with the temperature decreasing from the central region to the peripheral edge. This results in non-uniform etching of the wafer because the chemical etch rate or effectiveness is dependent on the temperature and the etch rate decreases with lower temperature for most of cases.
All drawings are schematic and are not to scale.